Hang on, politicians won't enforce sustainable living because the voters won't support it, but violent global revolution (presumably from a voting-minority?) does it?
And the "save the planet" faction (which we might think are left-leaning) overlap with the mostly non-violent faction? Whole the conservative drill-baby-drill faction overlap with the gun-loving, govt overthrowing militant types?
So your second possibility doesn't pass the smell test.
And of course we won't destroy the planet. At worst we'll make it unsuitable for human life. The planet itself will be just fine, and life will thrive after-people just like it does everywhere people have left.
Yes, I think the planet will change. And those people unable to adapt will perish. But plenty of people will survive, just perhaps not with current US lifestyles...